Referring to FIG. 1, a shoe sole 1 is illustrated. The shoe sole 1 has an attachment surface 11 that is to be attached to other part(s) of a shoe, and a sidewall 13 that surrounds a circumference of the attachment surface 11 and that has an inner surface 132 adjoining the attachment surface 11. In the manufacturing process of a shoe, the attachment surface 11 and the inner surface 132 are applied with a certain amount of glue, and a conventional approach of inspecting the certain amount of glue is by visual inspection. However, the conventional approach may be inefficient and error-prone.